Typical materials requiring surface flatness at high level include a single-crystal silicon disk called a silicon wafer for producing semiconductor integrated circuits (IC, LSI). The surface of the silicon wafer should be flattened highly accurately in a process of producing IC, LSI etc., in order to provide reliable semiconductor connections for various coatings used in manufacturing the circuits. In the step of polishing finish, a polishing pad is generally stuck on a rotatable supporting disk called a platen, while a workpiece such as a semiconductor wafer is stuck on a polishing head. By movement of the two, a relative speed is generated between the platen and the polishing head while polishing slurry having abrasive grains is continuously supplied to the polishing pad, to effect polishing processing.
As polishing characteristics of a polishing pad, it is requested that a material being polished is excellent in planarity and in-plane uniformity and a polishing rate is large. A planarity and in-plane uniformity of a material being polished can be improved to some extent with a polishing layer higher in elastic modulus. A polishing rate can be bettered by increasing a holding quantity of a slurry on a foam with cells therein.
For example, Patent Document 1 discloses a polishing cloth for use in planarizing a material having a step, which includes a polishing surface having parts with different degrees of surface hardness, wherein the parts with different degrees of surface hardness are formed by phase separation of resin that forms the surface.
Patent Document 2 discloses a polishing pad useful for planarization, which includes a polymer matrix containing a dispersed elastomeric polymer and having a glass transition temperature higher than room temperature, wherein the elastomeric polymer has an average length of at least 0.1 μm in at least one direction, makes up 1 to 45% by volume of the polishing pad, and has a glass transition temperature lower than room temperature.
Considering the development of next-generation devices, there is a demand for high-hardness polishing pads capable of further increasing planarity. In order to increase planarity, non-foamed, hard polishing pads may also be used. In the case where such hard pads are used, however, a problem may occur in which scratches (scars) are more likely to occur on the surface of the material being polished.
Patent Document 3 discloses a polishing pad for use in polishing Cu films, which has a polishing layer made of a polyurethane resin foam so that scratching can be less likely to occur, wherein the polyurethane resin foam is a product of curing reaction of a chain extender with an isocyanate-terminated prepolymer containing an isocyanate component and a high-molecular weight polyol component as raw material components, and the high-molecular weight polyol component contains 30% by weight or more of polyester polyol.    Patent Document 1: JP-A-08-11050    Patent Document 2: JP-A-2008-173760    Patent Document 3: JP-A-2007-42923